This invention pertains to glass fiber suitably available for non-woven fabric base material of a laminate and also to a method of producing a laminate comprising such glass fiber non-woven fabric base material.
Glass fiber is produced by spinning while molten glass is extruded through fine holes in a bottom of a platinum pot called a bushing. A number of glass fibers are tightly bound and wound, before which a surface of glass fiber is treated by sizing agent.
Glass fiber non-woven fabric or mat available for base material of a laminate is produced by paper-making after the bound glass fibers are finely cut into glass chopped strands and dispersed in white water. The bound glass chopped strands should be essentially scattered and homogenously dispersed in white water.
Thus, it will be noted that the sizing agent on the surface of the glass chopped strands is required to have functions of promoting the dispersibility of glass chopped strands and also of preventing the dispersed glass chopped strands from cohering.
Conventionally, the sizing agent for glass fiber of laminate base material comprises compound including water soluble polymer such as starch, acrylic amide vinyl acetate copolymer, carboxymethyl cellulose and polyvinyl alcohol, dispersing agent such as cationic fatty acid amide and silane coupling agent such as epoxy silane.
However, the glass chopped strands on the surfaces thereof having the conventional sizing agent cannot be fully dispersed in white water when glass fiber non-woven fabric or mat is produced. The thus produced glass fiber non-woven fabric has a number of glass chopped strands included while being tightly bound.
As such glass fiber non-woven fabric is impregnated with resin varnish and dried to produce prepreg, the portion of the glass fiber non-woven fabric including the glass chopped strands tightly bound tends to fail to be impregnated with resin or to be insufficiently impregnated with resin.
A laminate of glass fiber non-woven fabric base material formed by deforming such prepregs under heat and pressure has heat applied to form an electrically insulating board, but it tends to blister at the portion of the laminate including the tightly bound glass chopped strands.
The laminate of glass fiber non-woven fabric has insufficient characteristics of moisture resistance and electrical insulation for the electrically insulating boards. Of late, a wiring pattern of a printed board has a high density and is required to have a distance of 0.3 mm between through holes and to have improved characteristics of moisture resistance and electrical insulation in view of prevention of migration. Thus, it will be noted that the laminate of conventional glass fiber non-woven fabric could not be used for the printed board because it had poor characteristics of moisture resistance and electrical insulation.